1. Field of the Invention
The present invention relates to nonreciprocal circuit devices, and in particular, to a nonreciprocal circuit device such as an isolator or a circulator for use in microwave bands, and a communication apparatus including the nonreciprocal circuit device.
2. Description of the Related Art
In general, a lumped-constant isolator for use in a mobile communication apparatus such as a mobile phone has a function of allowing signals to pass only in a transmission direction so that a reverse transmission of the signals is prevented.
A lumped-constant isolator as shown in FIG. 7 is known (see Japanese Unexamined Patent Application Publication No. 11-298205) as a lumped-constant isolator of the above type. A lumped-constant isolator 200 in FIG. 7 includes a metal upper case 250 made of magnetic metal, a permanent magnet 260, a central electrode assembly 240, a terminal case 230, a metal lower case 220 made of magnetic metal, a spacer 280, a termination resistor R, and matching capacitors C11, C12, and C13.
The central electrode assembly 240 is formed such that three central electrodes 271 to 273 are arranged above a ferrite member 270 so as to cross at an angle of approximately 120 degrees with respect to one another, with an insulating sheet provided therebetween. On the upper surface of the spacer 280, an inductor pattern L10 is formed. The inductor pattern L10 and an external capacitor (not shown) outside the isolator 200 which is electrically connected to the isolator 200 constitute a band-pass filter. This band-pass filter is connected to the input side of the isolator 200, and has a function of reducing a high frequency distortion and unnecessary radiation by increasing the amount of attenuation out of the operating frequency of the isolator 200, particularly in high frequency bands (the second harmonic and the third harmonic).
As for conventional mobile communication apparatuses, a reduction in thickness and weight is in great demand, due to their uses. This is accompanied by a demand for a reduction in the heights of isolators. In one method for meeting the demand, it is possible that the distance between the central electrode assembly 240 and the permanent magnet 260 be reduced. However, by reducing the distance between the central electrode assembly 240 and the permanent magnet 260, a problem occurs in that a space for the spacer 280 provided with the inductor pattern L10 cannot be secured.
Because the inductor of the band-pass filter must be disposed in a small space between the central electrode assembly 240 and the permanent magnet 260, the inductor is limited to a planar type. Accordingly, it is impossible to employ, as the inductor of the band-pass filter, a wire-wound inductor and a laminated inductor (chip inductor) which have large heights. This causes a small degree of freedom in band-pass filter design.
Accordingly, it is an object of the present invention to provide a nonreciprocal circuit device having a low height and a high degree of freedom in design, and a communication apparatus including the nonreciprocal circuit device.
To this end, according to an aspect of the present invention, there is provided a nonreciprocal circuit device including: a permanent magnet; a ferrite member to which a direct current magnetic field is applied by the permanent magnet, the ferrite member having a plurality of central electrodes; an electric-circuit-component assembly electrically connected to at least one of central electrodes, the electric-circuit-component assembly including at least one electric circuit component; a resin case for accommodating the central electrodes, the electric-circuit-component assembly, and the ferrite member; and a metal case for accommodating the permanent magnet, the ferrite member, and the central electrodes, wherein the electric-circuit-component assembly is provided on a side of the permanent magnet; and the electric-circuit-component assembly is disposed below the upper surface of the permanent magnet in parallel to the thickness direction of the permanent magnet and has a portion overlapping with the permanent magnet.
Preferably, the electric-circuit-component assembly includes an inductor.
The inductor may be one of a wire-wound inductor and a laminated inductor.
The permanent magnet may be either square or circular.
The electric-circuit-component assembly may be one of a low-pass filter, a high-pass filter, and a band-pass filter.
A communication apparatus according to another aspect of the present invention includes at least one of the above nonreciprocal circuit devices.
According to the above-described construction, the distance between the central electrode assembly and the permanent magnet can be reduced because the electric-circuit-component assembly is disposed on a side of the permanent magnet. This enables the nonreciprocal circuit device to have a low height.
By forming the permanent magnet in a shape such as a square or a circle so that the permanent magnet covers the ferrite member, the distribution of a direct current magnetic field applied to the ferrite member can be uniformly maintained.
The electric-circuit-component assembly includes one of a low-pass filter, a high-pass filter, and a band-pass filter, thereby having a function of reducing a high frequency distortion and unnecessary radiation by increasing the amount of attenuation out of the operating frequency of the nonreciprocal circuit device.
In addition, the communication apparatus includes the nonreciprocal circuit device having the above-described characteristics, whereby its thickness and weight can be reduced.
According to the present invention, by disposing an electric-circuit-component assembly on a side of a permanent magnet, the distance between a central electrode assembly and the permanent magnet can be reduced, whereby the heights of a nonreciprocal circuit device and a communication apparatus can be reduced. The electric-circuit-component assembly does not need to be provided in a small space between the permanent magnet and the central electrode assembly, so that electric circuit components such as an inductor do not need to be limited to a planar type, and a wire-wound inductor and a laminated inductor (chip inductor), which have large heights, can be employed. As a result, the degree of freedom in band-pass filter design increases.